The chemical vapour deposition (CVD) process was invented in the 1970s and has been continuously improved over the decades in order to respond to ever more demanding market requirements in terms of the coating process, structures and combinations.
The typical process temperature for classic CVD coatings is between 720° C. and 1050° C. The most common items coated are punches, metal forming tools, and extrusion dies. In terms of substrate materials due to the high temperature of the process, most steels will require a post coating heat treatment. The coatings typically deposited are TiC, TiCN, Al203. The coatings are almost always deposited as multi-layers.
The advantages of the process include                Possibility to coat complex geometries, including certain inner diameters        High loading capacity of certain tools (but long cycle times)        Items to be coated do not require rotation within the retort        Excellent coating uniformity, independent of part geometry        Extreme toughness of coatings        
Initially CVD is known as heat-activated process which relies on the reaction of gaseous chemical compounds with suitably heated and prepared substrates. As it is written above it requires high substrate temperatures. To decrease the substrate temperature the different techniques initiating molecules decomposition (cracking) have been used. Most common this is the radio frequency (RF) initiated discharge in the process chamber, see the published Japanese patent application 20062700979. Among other techniques microwave CVD reactor, see the published U.S. patent application 2007/036895, DC CVD reactor, see the South Korean patent document KR960014905B, hybrid RF and DC reactor, see the South Korean patent document KR960012316B, pulse reactor, see the published Japanese patent application 2004244713, and others can be mentioned. Electric discharges in a CVD reactor results in ignition of the plasma. Therefore these kinds of the CVD are called plasma activated CVD (PA CVD) or plasma enhanced CVD (PE CVD). The use of PA CVD results in a significant reduction of the work piece temperature. It is for PA CVD in the range 100°-300° C. (compare to classic CVD). Since the electric discharges are used problems associated with the arc suppression and work piece biasing may be important, see the published International patent application WO 2007/024765 and the published Japanese patent application 2006093342.
The second problem in CVD technology is the CVD reactor design and optimization. The following main reactors geometry design can be mentioned.                The showerhead reactor, see the published U.S. patent application 2004127067        The tube reactor, see the published International patent application WO 01/61070        
The reactor design varies according to the methods of plasma excitation used.
One of the important parts of the reactor is the cathode used in the electric discharge. In recent years magnetron-like cathodes have been used, see the published Japanese patent applications 2005/022950 and 2005/272948. The magnetron cathodes are typical parts of the physical vapour deposition (PVD) technology and devices. From this point of view the reactor combines CVD and PVD principles and can therefore be called a hybrid CVD-PVD reactor.
So, as one can see the active development of the CVD methods and devices is continuing over several decades. Still further development is required in all mentioned areas of the CVD technology. They include in particular: methods of the plasma excitation, reactor design and optimization, arc suppression and work pieces biasing.
The PA CVD, PA PVD and hybrid technologies are generally used for deposition of material layers onto work pieces. One of the decisive parameters is the deposition rate. The characteristic value of this parameter described for example in the published Japanese patent application 2006/270097 cited above is 790 nm/min. The plasma generation is accomplished by RF discharges. Modern technology requires deposition rates that are 10-20 times higher in order to deposit thick layers of about 1000 μm on the work pieces having large surfaces of complex shapes. Therefore, a crucial parameter is the cost of an industrial CVD coating machine. To achieve chip and efficient deposition using RF and microwave techniques is too expensive for work pieces of complex shapes requiring a large space.
The cheapest solution is the DC principle. The week side of this technique is the low deposition rate because of the low discharge current between the electrodes. To increase the discharge current a cathode having an enhancing magnetic field is used, see the published Japanese patent applications 2005/272948 and 2005/022950 cited above. Still this method is not enough to achieve a deposition rate more than about 10 μm/hour.
However, in the PA PVD technology high current magnetron sputtering is widely known, see U.S. Pat. No. 6,296,742, the published International patent application WO 2006/049566 and the published U.S. patent application 2004/020760. The week side of high current magnetron sputtering is the fact that by increase of the discharge current the deposition rate proportionally decreases, compare the published International patent application WO 2005/050696, FIG. 2a. On the other side, the sputtered vapour ionization increases.
There are five main problems that may have to be solved in order to achieve efficient use of high current low duty cycle electric discharges for complex molecules decomposition in a CVD reactor.    1. High plasma density. The decomposition in PA CVD is produced by molecules colliding with electrons available in plasma. After decomposition radicals consisting of solid species such as Si, C are deposited onto work pieces. To achieve a high deposition rate it is necessary to get a high electron density in the generated plasma. Because of the general quasi-neutrality of plasmas it means that it is necessary to achieve a high plasma density. This can be achieved by pulsed, high current, low duty cycle electric discharges between electrodes in a PA CVD reactor    2. High electron energy. It is necessary to achieve an electron energy sufficient for molecules decomposition. The characteristic energy required is in the range of few electronvolts up to a few dozens of electronvolts    3. Low cathode erosion. Because of the sputtering effect the cathode of discharge gap is eroded which results in the necessity for periodically replacing the cathode with a fresh one. Actually, the deposition rate from cathode sputtering is less than 10% of the total deposition rate. It is still a significant portion and the parasitic effect of cathode sputtering hence has to be minimized.    4. Electrode design. In most applications the deposited layers of materials have a very low electrical conductivity or are almost dielectric. These materials cover the surfaces of the electrodes and make them electrically non-conductive. The main part of problem relates to the anode of the discharges since the cathode can be sufficiently cleaned by sputtering. The dielectric layer makes the discharges impossible. This phenomenon is also parasitic and a specific electrode design is required.    5. Arc suppression. Existence of layers having a low electric conductivity or dielectric layers at the electrodes also results in a random transformation of diffused glow discharges into arc discharges. It destroys the deposition process and layers on the work pieces. Therefore, arc suppression is required.